Display systems that are mounted on eyewear or head gear are known in the art. Such display systems may be mounted onto eyeglasses, spectacles, goggles, helmets, and the like, or otherwise supported before a viewer to present an image from a display device to the viewer. Display systems may be used in a variety of different applications. For example, one such application is a virtual display terminal, in which a user views video data from a portable device, such as a Digital Video Disc (DVD) player or a high end game station. Another application is a Head-Up Display (HUD) in the cockpit of an aircraft, in which a pilot views flight related information (e.g., altitude, airspeed, heading) while maintaining external situational awareness.
There are two general categories of display systems: see-through systems and opaque systems (i.e., non see-through systems). In see-through systems, the display image is combined with the ambient scenery, enabling the user to view both the display image and the ambient scene simultaneously. Usually, the display image appears superimposed onto an image from the ambient scene. In opaque systems, the display image blocks out the ambient scene, either partially or completely, so that the user is unable to view at least a part of the ambient scene. See-through display systems serve to minimize user obscuration and are useful for applications where it is important that the user does not miss any information from the external environment. However, see-through display systems inherently reduce the amount of energy passing from the display device to the eye of the user (i.e., to enable transmission of ambient light), resulting in a poor contrast ratio between the display image and the ambient scene. See-through display systems also tend to be somewhat bulky and cumbersome, owing to the general dimensions of the display device and the optical elements that are directed to eliminating distortion.
In contrast, opaque display systems generally have a simple overall assembly, although they tend to introduce physical discomfort to the user, mainly due to the loss of situational awareness (i.e., since the opaque display obstructs visibility of the scene to a selected eye of the user, depriving scenic details from the user, thereby reducing the ability of the user to understand and react to events occurring in the surrounding area). For example, in monocular opaque display systems, the user may suffer from eye rivalry (i.e., when the images provided to each eye are mutually exclusive and have no common points for the brain to sufficiently link the two into a unified image, the visual perception of the viewer alternates between the views seen by each eye). Since human factor issues, such as user comfort, are critical, see-through display systems are usually preferred over opaque display systems.
Several existing display systems have small general dimensions but do not provide a wide enough field of view for viewing the display image. Other small see-through display systems do not provide sufficient eye-relief, for allowing correcting spectacles (e.g., eyeglasses) in between the eye and the eyepiece of the display system. Some display systems have a small eye motion box (i.e., exit pupil diameter), which results in image loss if the display moves during use. Some display systems have low display brightness, causing a low contrast ratio in conditions with high ambient light levels. Other features play a key role in the quality and overall performance of the display system, such as the system dimensions, weight, center of gravity, display resolution, color correction, contrast, optical focal length, obscuration, and the like.
One technique for obtaining the required focal length in a compact visual system, commonly used in binoculars, small telescopes, and occasionally in cameras, involves a pair of Porro prisms. A Porro prism is a block of glass, triangular in cross-section, with angles of 45°, 45° and 90°. Reference is now made to FIG. 1, which is a schematic illustration of a double Porro prism assembly, generally referenced 10, which is known in the art. Double Porro prism assembly 10 includes a pair of Porro prisms, referenced 12 and 14. The three surfaces of first Porro prism 12 are referenced 16, 18 and 20, respectively. The three surfaces of second Porro prism 14 are referenced 22, 24 and 26, respectively. Porro prisms 12 and 14 are arranged such that the long surface 20 of first Porro prism 12 is adjacent to the long surface 26 of second Porro prism 14. An incoming light beam enters first Porro prism 12 via surface 20, at a substantially vertical direction, along path 30A. The incoming light beam is incident upon surface 16, which internally reflects the light beam at a substantially horizontal direction along path 30B toward surface 18. Surface 18 internally reflects the light beam to second Porro prism 14 at a substantially vertical direction, along path 30C. The light beam exits first Porro prism 12 via surface 20 and enters second Porro prism 14 via surface 26. The light beam is then incident upon surface 22, which internally reflects the light beam at a substantially horizontal direction along path 30D toward surface 24. Surface 24 then internally reflects the light beam at a substantially vertical direction along path 30E toward surface 26, upon which the light beam exits double Porro prism assembly 10. Overall, the light beam undergoes a total of four reflections within double Porro prism assembly 10. It is noted that in a double Porro prism assembly, the incoming axis and the outgoing axis of the light beam are not aligned. Porro prisms provide minimal light loss and image degradation, but are typically large and bulky and require a large housing.
Conventional eyepieces in display systems use a single beam combiner, or an equivalent optical element (e.g., a partially transparent lens or mirror), to direct the light from the display image and the light from the ambient scenery toward the eye of the user. Reference is now made to FIG. 2, which is a schematic illustration of a single beam combiner eyepiece, generally referenced 50, which is known in the art.
U.S. Pat. No. 5,348,477 to Welch et al entitled “High definition television head mounted display unit”, is directed to a head mounted non-pupil forming display system which uses a projection screen to produce a replica of an image for viewing by an observer. The display system includes an imaging source, a fiber optic cable, a relay lens, and an optical assembly. The optical assembly includes a projection lens, a rear projection screen, a beam splitter, a plurality of mirrors, and an eyepiece. The rear projection screen includes a left rear projection screen associated with the left eye of the observer, and a right rear projection screen associated with the right eye of the observer. The eyepiece includes a spherical mirror and a flat beam splitter. The imaging source may be a high definition television projector. The eyepiece is disposed in front of the eyes of the observer.
The imaging source generates an image and relays the image to the fiber optic cable through the relay lens. The fiber optic bundle transmits the image to the projection lens. Part of the output of the projection lens is deflected by the beam splitter to a first mirror, which reflects the light beam to the left rear projection screen. The left rear projection screen is on top of the part of the eyepiece in front of the left eye of the observer. The beam splitter deflects the remainder of the output of the projection lens to a second mirror, which reflects the light beam to a third mirror. The third mirror reflects the light beam to the right rear projection lens. The right rear projection screen is on top of the part of the eyepiece in front of the right eye of the observer. The relay lens includes optical elements to produce a correct mapping function, to ensure that the image seen through the eyepiece is essentially free of geometric distortion.
In another embodiment, the image is transmitted by two fiber optic cables. In a further embodiment, two image sources feed respective fiber optic cables through respective relay lenses. The replica of the image seen through the eyepiece by the observer seems to originate at a distance. The replica of the image may be combined with the direct view of objects seen through the eyepiece, such that the observer views the real world as well as the displayed image simultaneously.
U.S. Pat. No. 5,162,828 to Furness et al entitled “Display system for a head mounted viewing transparency”, is directed to a display system for conventional eyewear having a transparency that defines a field of view. The display system projects a magnified image of displayed information at a distance from the user, in the field of view defined by the transparency. The user may be, for example a skier or scuba diver, wearing conventional eyewear, such as goggles or a dive mask. The conventional eyewear has a frame that supports a transparency, such as a lens. The display system includes a Liquid Crystal Display (LCD) display and optics. The LCD display is mounted on the frame supporting the transparency. The optics is also mounted on the frame.
The LCD display displays information, preferably information relating to the activity for which the head mounted viewing transparency is worn. For example, the information may include the speed of a skier as sensed by a speed sensor. The optics includes a planar mirror and a collimating lens. The planar mirror is disposed in the periphery of the normal field of view defined by the transparency. The planar mirror receives the information and reflects the information to the collimating lens. The collimating lens collimates the light to project an image of the information depicted on the LCD display, so that the image appears located at a distance from the user when viewed from the planar mirror. Alternatively, the optics includes a toroidal mirror. The toroidal mirror receives the information from the LCD display and collimates the light, thereby projecting an enlarged image of the information in the periphery of the field of view. The mirror may be fully reflective. Alternatively, the mirror may be partially reflective, so as to superimpose the image of the displayed information on the scene viewed by the user through the transparency.
The LCD display includes a display plate, a backing plate, and a diffusing filter. The diffusing filter is exposed to ambient light, and provides an even illumination through the backing plate to the display plate, which is positioned adjacent to the diffusing filter. The display plate operates in transmissive mode, such that the portion of the display plate forming the characters is transparent, while the remainder of the display plate provides a dark background for the data characters. The ambient light diffused by the diffusing filter and transmitted to the display plate through the backing plate, illuminates the data characters to provide a contrast with the dark background. Alternatively, the display plate, the backing plate, and the diffusing filter may be replaced with active display elements, such as light emitting diodes.
The optical path defined by the relative position of the mirror, the LCD display, and the eyes of the user, may be made adjustable so that the display system can accommodate heads of various sizes. In one embodiment, the mirror is mounted on the transparency frame such that the position of the mirror is adjustable. In another embodiment, the position of the mirror is fixed, and the transparency frame includes adjustable temples to vary the optical path.
U.S. Pat. No. 4,867,551 to Perera entitled “Display projection optical system for spectacles or sunglasses”, is directed to a miniature display projection system that superimposes images from an opto-electronic display panel on to the normal field of view of a spectacles or sunglasses wearer. The display projection system is mounted on the upper part of the rim of a spectacles or sunglasses frame, standing on the outer part of the eyepiece. The display projection system includes a housing and a projection window. The housing is seated on to the rim of the spectacles or sunglasses frame via a slot on the bottom length of the housing, and secured with a fixing screw. The housing includes micro-electronics, an opto-electronic display panel, and a watch battery. The projection window is fixed to the housing and protrudes downwards. The micro-electronics generate display information. The opto-electronic display panel produces visual images. The watch battery provides electrical power to the micro-electronics and the opto-electronic display panel.
The projection window is made of thin optically transparent material. The bottom end of the projection window is curved and slanting away from the eyepiece of the spectacles or sunglasses. The curved portion is referred to as the active portion of the projection window, and has the shape of an oblong sectional part of a parabolic surface. The concave side of the parabolic surface faces inward toward the eye of the wearer. In another embodiment, the projection window stands between the eye and the eyepiece of the spectacles or sunglasses.
The opto-electronic display panel may be of light emitting diode (LED) type or liquid crystal display (LCD) type. An LCD type display may include an active matrix technology display, enabling a television reception unit to be carried externally and connected to the display panel. The displayed may be, for example, time of day or television images. The surface of the opto-electronic display panel may be slanted for optimum projection angle. The opto-electronic display panel may be adjusted up or down inside the housing. The opto-electronic display panel display surface faces down and open to the outside of the housing. A micro switch activates the opto-electronic display panel, whenever the user wishes to view the display. Further micro switches coupled to the micro-electronics enable the presenting or selection of display information parameters and functions.
The active portion of the projection window intercepts light rays emanating from the surface of the opto-electronic display panel, and partially reflects the light, projecting the light parallel toward the eye of the spectacles or sunglasses wearer. Light from the normal field of view of the spectacles or sunglasses is transmitted through the thin transparent projection window with no distortion or obstruction. The wearer sees a virtual image of the display superimposed on the normal field of view, whenever the display is activated. When the display is not activated, the wearer does not see the projected display in the normal field of view.
U.S. Pat. No. 5,886,822 to Spitzer entitled “Image combining system for eyeglasses and face masks”, is directed to an image combining lens system for integrating within eyeglasses or a facemask, that provides the optical functions of a head-mounted display system in a compact form. The image combining lens system includes an image source or display, a lens system, and an eyeglass frame or face mask.
The display and a first lens are mounted at the edge of the lens system, or main lens. The main lens is an optical system comprising embedded lenses and other optical components and surfaces, and includes an insert. For example, the main lens may be an eyeglass lens, with or without vision-correcting optical power. The insert comprises two materials having different indices of refraction. Light rays from the display travel via the first lens, through the material of higher refractive index of the insert, and are incident upon the interface between the two materials of the insert. The light rays from the display are totally internally reflected toward a third lens, positioned adjacent to the eye of the user. Ambient light rays travel through the material of lower refractive index of the insert, and are incident upon the interface, which refracts the ambient light rays away from the third lens. Alternatively, the insert comprises materials having thin-film interference coatings at the interface, and the interface serves to combine the display light and the ambient light. The first lens and third lens are selected such that the combined optical power forms a microscope, allowing the image from the display to be viewed with a desired magnification.
The display may be located remote from the main lens, using an image relay, such as a coherent optical fibre bundle or a gradient index lens image conduit, to relay the display image to the main lens. For example, the display may be located behind the head of the user. In another embodiment, the insert comprises a cube beam splitter, which is used as a combiner, instead of an interface having a totally internally reflecting surface. The cube beam splitter does not refract the ambient rays. The cube beam splitter reflects approximately 50% of the ambient light and display light to the eye of the user. However, a polarizing beam splitter, used together with a display that provides polarized light, allows higher reflection percentages to be obtained. A housing holds two glass plates that are joined to the cube beam splitter. The main lens includes the glass plates, the cube beam splitter, and other internal parts, such as two optional polarizing layers. Ambient light rays pass through the main lens to the eye of the user via three possible paths, allowing for adjustment of the light level from the ambient scene reaching the eye, thereby balancing the light level between the display and the ambient scenery.
The image combining lens system may be designed as a see-through system (in which the display image is combined with the ambient image so that the user can see both images), see-around system (in which the display image occludes part of the ambient image), or full-immersion system (in which the entire ambient image is blocked so that the user sees only the display image). For example, an insert having interference coatings at the interface may be used for a see-through system, whereas an interface that provides total internal reflection may be used for a see-around system. Alternatively, the field of view of the insert may be increased and the main lens may be provided with an opaque cover, to form a full-immersion system.
U.S. Pat. No. 6,204,974 to Spitzer entitled “Compact image display system for eyeglasses or other head-borne frames”, is directed to a head-borne image display system that combines an image relay system and mechanical support with a mounting system that can be applied to eyewear or other head gear. The display system includes a support frame and a display assembly. The support frame is configured to be supported by the head of a user. The support frame supports the display assembly in front of the eye of the user. The display assembly includes a display element, an optical relay, and an eyepiece assembly. An optical pathway is located internally within the optical relay, to receive light from the display element. The optical relay is at least partially transparent to ambient light.
The display element provides a display image to the eyepiece assembly, passing through at least a portion of the optical pathway. Ambient light passes through two optical surfaces of the optical relay, toward the eye of the user. The eyepiece assembly is located within the optical relay, and has a partially or fully reflecting surface, which relays the display light out of the optical relay and toward the eye of the user. The display system may be a see-through system, so that the user sees a superposition of the display image and the ambient image. The optical relay and eyepiece assembly may include a combining element having, for example, totally internally reflecting surfaces, partially silvered mirrors or dielectric coatings, or holographic or diffractive surfaces with optical surfaces for vergence correction.
The display element may be mounted to a head-borne frame, such as an eyeglass frame, a face mask frame, or a head set, for example via a boom. The display assembly elements may be embedded within an eyeglass frame or lens. The display element may be added to or removed from the head-borne frame with little discomfort to the user. The display element may be located remote from the eyeglass lens, using an image relay, such as a coherent optical fibre bundle or a gradient index lens image conduit, to relay the display image to the main lens. The display element may be adjustable, allowing the user to position the display image in a convenient location within the field of view of the user.
The display system may include a housing assembly having a mounting mechanism, which can be mounted, in a removable manner, to the head-borne frame of the eyewear at a location outside the field of view of the user. The housing assembly may have circuitry to receive data or video signals. The housing assembly supports the display element, such as an electronic imaging assembly, outside the field of view of the user. The imaging assembly communicates with the circuitry in the housing assembly to produce an image.
U.S. Pat. No. 6,392,811 to Lindau entitled “Arrangement for a wearable optomechanical deflector for a display unit”, is directed to an optomechanical deflector for a line display unit, which has ocular and objective functions and components for sweep generation and image turning. The deflector includes a tilting plane mirror, a rigid cylindrical mirror or lens, and a concave mirror. The tilting mirror surface and rigid cylindrical mirror surface forms part of the objective function of the deflector. The concave mirror surface forms part of the ocular function of the deflector.
The tilting mirror receives incoming radiation from a line display unit, and reflects the radiation toward the rigid cylindrical mirror. The frequency of the tilting mirror is related to the line deflection function of the line display unit. The rigid cylindrical mirror surface reflects the received radiation toward the concave mirror. The concave mirror reflects the received radiation toward an eye of a viewer. The concave mirror surface reproduces the tilting mirror surface in the pupil of the eye of the viewer.
The objective function of the deflector is positioned at a distance from the ocular function, so that the deflector has an afocal optical system. The tilting mirror, which performs sweep generation, may also be arranged to perform image turning, so that an image turned appropriately is directed upon the pupil of the eye of the viewer. The tilting mirror may be arranged in front of the forehead of the viewer. The tiling mirror may be positioned upwards, downwards, or toward the side. In another embodiment, the tilting mirror and the rigid cylindrical mirror have changed places. The concave mirror may be replaced with a partly transparent mirror, enabling the viewer to view the surroundings and the image from the line display unit simultaneously.
U.S. Pat. No. 6,618,099 to Spitzer entitled “Display device with eyepiece assembly and display on opto-mechanical support”, is directed to a head-mounted display system with a transparent support fixture that suspends a display and an eyepiece near the eye of a user. The display system includes a display, a clear mechanical support fixture, and an eyepiece assembly. The eyepiece assembly includes a prism and a lens. The eyepiece assembly is positioned at one end of the support fixture. The display is positioned between the prism and the support fixture.
A light source transmits light through the support fixture, and incident on the back side of the display. The display modulates the light to form an image, and relays the image to the eye of an observer via the prism and the lens. The lens magnifies the image from the display, for convenient viewing. The observer also sees images from the ambient scene images, which pass through the support fixture, directly toward the eye of the observer.
The support fixture is elongated. The image from the display passes through the support fixture along the direction of elongation, while the image from the ambient scene passes through a clear side surface of the support fixture across the direction of elongation. The display is, for example, a transmissive LCD. In other embodiments, a reflective display or an emissive display may be used. The eyepiece assembly may also include a polarization beam-splitter coating, a quarterwave plate, and a focusing mirror, for collimating polarized light from the light source. In another embodiment, the support fixture is hollow, or has a thin plate shape, and conveys light from the light source to the display in free space along a straight path. The display system may further include a housing containing circuitry for electrical communication with the display and the light source. The display system may be mounted in front of one eye of the observer, via a fixture mounted to a spectacle frame or headband. A second display system may be used for viewing by both eyes of the observer. The display system may be provided with an ear piece and a microphone, to interface with a cellular telephone, computer, or personal digital assistant.